1. Field of the Invention
The present invention relates to a brake booster, and more particularly to a brake booster, in which a valve body and a poppet valve for regulating a flow of air of constant and variable pressure chambers are replaced by an integrated valve.
2. Description of Related Art
In general, a brake booster doubles a braking force applied to an input shaft using a difference between vacuum and atmospheric pressure, and then transmits the boosting force to an output shaft.
As illustrated in FIG. 1, a conventional brake booster includes a casing 10; a diaphragm 31 partitioning the casing 10 into a constant pressure chamber 21 and a variable pressure chamber 22; a stepped valve body 60, wherein one end thereof is slidably connected to the center of the diaphragm 31, the other end thereof protrudes to outside the casing 10, and an interior thereof is formed as a hollow cavity 63; an input shaft 40 located in the hollow cavity 63 of the valve body 60 to receive a pressing force generated by manipulation of a brake pedal; and an output shaft 50 transmitting a boosting force generated from the valve body 60 to a master cylinder.
The casing 10 is divided into the constant pressure chamber 21 and the variable pressure chamber 22 by the diaphragm 31. The force generated by a pressure difference between the constant pressure chamber 21 and the variable pressure chamber 22 is transmitted to a power piston 32, which abuts on the diaphragm 31. The centers of the diaphragm 31 and the power piston 32 are fixed to the valve body 60.
The constant pressure chamber 21 is provided with a vacuum connecting pipe 12, which communicates with an intake system of a motor vehicle engine, on outer wall of one side thereof. A return spring 80 is installed in the constant pressure chamber 21. Thus, when a brake is inactive, the diaphragm 31 and the power piston 32 will return to their original positions by an elastic restoring force of the return spring 80.
The input shaft 40 is a multistage shaft, a leading end of which is coupled with a plunger 70, which transmits the pressing force applied to the input shaft 40 to the output shaft 50. A reaction disc 51 made of elastic material is interposed between the plunger 70 and the output shaft 50. There is a predetermined gap between the plunger 70 and the reaction disc 51.
The input shaft 40 is located at the center of the valve body 60, which has a cylinder 65 into which the plunger 70 is slidably inserted in addition to the hollow cavity 63 serving as an external air inflow passage. In the hollow cavity 63, there are installed a poppet valve 64 regulating inflow of external air, and a poppet retainer airtightly fixing a rear end of the poppet valve 64 to an inner circumference of the hollow cavity 63. A return spring 23, that is a conical compressive coil spring, is installed between the poppet valve 64 and the step of the input shaft 40 so as to return the input shaft 40 in a backward direction (i.e. to the left).
This motor vehicle brake booster is configured in such a manner that the constant and variable pressure chambers are kept in a vacuum state by the intake system of the motor vehicle engine. In this state, when a driver steps on a brake pedal, the input shaft 40 advances to the left, and thus the external air rapidly flows into the variable pressure chamber 22 in a loaded state through the valve body 60. As a result, the variable pressure chamber 22 is kept under atmospheric pressure. When the variable pressure chamber 22 is kept under atmospheric pressure, there occurs a pressure difference between the variable pressure chamber 22 under atmospheric pressure and the constant pressure chamber 21 under negative pressure. Due to this pressure difference, the power piston 32 is pushed toward the constant pressure chamber 21. At this time, the valve body 60 connected to the power piston 32 moves together, and pushes the output shaft 50. The output that is more amplified than the input by this operation is transmitted to a master cylinder assembly through the output shaft, and thus braking hydraulic pressure is generated.
When the driver releases the brake pedal, the input shaft 40 returns to its original position by the elastic restoring forces of the return spring 80 and the power piston 32. In addition, the air of the variable pressure chamber 22 flows out to the constant pressure chamber 21 under vacuum through a vacuum passage, and the air of the constant pressure chamber 21 flows out to the outside through the vacuum connecting pipe 12 and a vacuum hose. As a result, the brake booster enters an initial state.
As described above, the conventional brake booster employs the valve body 60 and the poppet valve 64 in order to control the intake of the air. Thus, the number of parts is relatively increased, and thus assembly and management of parts are complicated. Consequently, the overall productivity of the brake booster is lowered.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.